Method for production of acrylic composite fiber

ABSTRACT

A METHOD OF PRODUCING ACRYLIC COMPOSITE FIBERS HAVING EXCELLENT BULKINESS AND WOOL-LIKE HAND BY CONJUGATE SPINNING OF A SOLUTION OF AN ACRYLONITRILE POLYMER AND A HEATTREATED SOLUTION THEREOF IN THE PRESENCE OF A CONCENTRATED AQUEOUS ZINC CHLORIDE SOLUTION AS THE SPINNING SOLVENT.

Filed Aug.

FIG. I

1972 MASATOSHI YOSHIDA ETAL 3,701,819

mmmon FOR PRODUCTION OF ACRYLIC COMPOSITE FIBER 14, 1969 2 Sheets-Sheet 1 6b 7b ab I60 TEMPERATURE m I O 20 150 0 I20C C mr'fil lfim 0.o|% YASUO SAJI 5 I u l fm ee'lfil 0.005% I i BY M,

. ATTORNEYS TIME (min) Oct. 31, 1972 MASATOSHI YOSHTIDA ET AL ,8

METHOD FOR PRODUCTION OF ACRYLIC COMPOSITE FIBER 2 Sheets-Sheet 2 Filed Aug.

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BEE I United States Patent Office Patented Oct. 31, 1972 3,701,819 METHOD FOR PRODUCTION OF ACRYLIC COMPOSITE FIBER Masatoshi Yoshida, Shizuoka, Yasuo Saji, Nakatogari, and Kazuhisa Saito and Shigeru Ikegami, Kamitogari, Japan, assignors to Toho Beslon Co., Ltd., Tokyo,

Japan Filed Aug. 14, 1969, Ser. No. 850,036 Claims priority, appligatior rggpan, Aug. 16, 1968,

US. Cl. 264-168 13 Claims ABSTRACT OF THE DISCLOSURE A method of producing acrylic composite fibers having excellent bulkiness and wool-like hand by conjugate spinning of a solution of an acrylonitrile polymer and a heattreated solution thereof in the presence of a concentrated aqueous zinc chloride solution as the spinning solvent.

BACKGROUND OF THE INVENTION (1) Field of the invention The invention relates to the production of composite fibers.

(2) Description of the prior art Hithertofore, various methods have been proposed to improve fabric properties by imparting spiral crimps to artificial fibers. In the field of acrylic fibers, spiral crimps are usually prepared by spinning together two different types of polymer solutions to form a composite fiber. If the two components employed possess different contraction behaviors under heating or other special conditions, spiral crimps may then be obtained by suitable treatment after spinning. The crimping properties of a composite fiber may thus depend upon the difference between the polymeric chemical constituents, the spinning procedure, treatment conditions and the like.

However, as compared with the production of conventional acrylic fibers, it requires higher expense and more complicated processes to produce a composite fiber, primarily because two different types of polymer solutions must be prepared. Further, the preparation for polymerization, polymerization dissolving, deaeration and fitering must all be ordinarily doubled.

SUMMARY OF THE INVENTION However, the applicants have found that a composite fiber having satisfactory crimping properties can be produced comparatively simply and economically merely by the conjugate spinning together of a solution of acrylonitrile polymer and a heat-treated solution thereof.

DETAILED DESCRIPTION OF THE INVENTION An acrylic fiber shows a characteristic thermal contraction behavior in aqueous 80% (v./v.) dimethyl formamide solution as shown in FIG. 1 and the structural characteristics of the fiber, such as orientation, cohesive structure and polymer composition reflect on the shape of the contraction curve. The temperature at maximum contraction of a fiber (T is lowered as heat treatment of the polymer solution is increased, mainly because of chemical changes. We have found that composite fibers with satisfactory spiral crimping properties may be produced by conjugate spinning together of a polymer solution and the heat treated polymer solution thereof, wherein the difference in T of the fibers produced from the two solutions is more than 5 C.

According to this invention, the thermal change of the polymer solution is carried out at a temperature of 60 150 0, preferably -130" C. in the presence of concentrated aqueous zinc chloride solution as the solvent wherein a basic compound is present in an amount of 0005-02 wt. percent, calculated as zinc oxide. The higher the temperature and the larger the amount of basic compound present, the faster the thermal change proceeds. When the amount of basic compound present is less than 0.005% as zinc oxide, it requires too long a time to obtain the desired heat-treated solution on an industrial scale. On the other hand, when the amount of basic compound present is more than 0.2%, the thermal change proceeds at an uncontrollably fast rate. Such a large amount of basic compound also inhibits polymerization, particularly when a peroxide is used as the polymerization catalyst in solution polymerization.

In determining the concentration of the basic compound, the concentrated aqueous zinc chloride solution is taken up by 10 gr. as pure zinc chloride constituent to be added in about 10 ml. of water and then several drops of the indicator, methyl orange solution (0.1%) is added to the resulting solution. By titration of 1 N hydrochloric acid, the basic compound concentration can be calculated from the following equation from the color changing point of the indicator:

wherein C represents the basic compound concentration (percent wt.), S represents the weight in grams of the material being tested and D is the amount of 1 N hydrochloric acid used (ml.). Among such basic compounds which may be employed, there may be mentioned zinc oxide, zinc carbonate, sodium hydroxide, sodium carbonate, ammonium hydroxide etc. Zinc oxide and zinc carbonate are preferred for use with the zinc chloride solution of this invention. When the salt solution contains an excess amount of basic compound, it may be adjusted to a desired concentration by adding hydrochloric acid.

In order to clarify the effect of heat treatment on the T of the resulting fiber, test results are given in Table 1, wherein aqueous 57% zinc chloride'solution, containing 0.05% zinc oxide as the basic compound was used as the solvent, and a copolymer of acrylonitrile-methyl acrylate (:10, molecular weight-=7.2 10 was used. When the polymer solution (polymer concentration is 10 wt. percent) was heated at 110 C., the viscosity and transparency of the polymer solution and the T of the resulting fiber changed as shown in the table.

TABLE 1.THE EFFECTS OF HEATING TIME (AT C.)

Heating time Viscosity l Transparency 2 TI nun.) oise) (percent) C.)

1 Measured at 45 C. 2 Measured at 420 my using cell of 2 cm. width.

It is clearly shown in Table 2 that, when the difference in T is more than 5 C., the resulting composite fiber has characteristic crimp properties, good bulkiness and a wool-like hand feeling.

When thermal change proceeds to excess, i.e'. the difference in T is more than 15 C., the resulting composite fiber is not suitable for fabric uses because of excessive crimps, which result in a hard hand feeling.

TABLE 2.-CRIMP PROPERTIES OF COMPOSITE FIBERS Crimping proserties of composite FIGS. 2 and 3 illustrate the effects of treatment temperature and concentration of zinc oxide, respectively, on the difference in T obtained. Thus, any desired difference in T can be adjusted by controlling the heating temperature, heating time or basic compound concentration in the solvent used.

When the basic compound concentration is kept constant, the effects of heating temperature and time on the difference in T are approximately expressed as in the formula:

AT =A t exp (B/T) wherein t represents heating time, T heating temperature (K) and A and B are constants.

The inventors have found that the most suitable number of crimps in a composite fiber is not always fixed, but depends on the type of end use contemplated. In a conventional method of composite fiber production, when the number of crimps is desired to be changed, the polymer composition or conditions of aftertreatment must be changed. However, the process of the invention provides that it may be easily carried out by changing of heating temperature or time.

As the viscosity of polymer solution gradually decreases with the proceeding of the thermal change, as shown in Table 1 (1--77/71.) can be taken as a measure of thermal change, wherein a1. and 1; are defined as the viscosity of the original polymer solution and the heat-treated solution respectively. Absorption at 1610 cm. in infra-red spectrum may also be used as a measure of thermal change.

Another feature of the composite fiber produced by the method of this invention is the excellent laminating property of the two components to each other. Generally, when two difierent types of polymers are spun side by side to form a composite fiber, there is a tendency to delaminate, perhaps because of poor compatibility of the two components. This tendency is more noticeable when the chemical compositions of the components must differ considerably in order to improve the crimping properties of the fiber. Such delamination results in loss of crimping properties and deterioration of fabric qualities. However, the laminating property of the composite fiber produced by the present invention is good, perhaps because the two components originate from the same polymer solution.

Dyed end products made from conventional acrylic composite fibers often have a nettled appearance owing to different take-up of dye in the two components, but such unfavorable appearance is not observed in the composite fibers of this invention.

The solvent used in the present invention is a concentrated salt solution containing zinc chloride as the main constituent. Other constituents, such as sodium chloride, magnesium chloride, ammonium chloride, etc. can be added if desired. The total salt concentration is preferably in the range of 50-65 wt. percent.

The original polymer solution can be prepared by dissolving the polymer produced by a conventional suspension polymerization or, more preferably, by solution polymerization in the solvent.

In order to carry out solution polymerization, peroxides such as ammonium persulfate, sodium persulfate and hydrogen peroxide as well as redox systems such as sodium persulfate-sodiurn bisulfite and sodium chlorate-sodium methabisulfite may be used as polymerization catalysts.

A continuous process, employing solution polymerization with heat treatment of the resulting polymer solution is preferred for industrial operation, rather than a batchwise process. Applicants have further found that a homogeneous polymer solution can be prepared without the production of foam or gel-like substances and can be directly used as a spinning solution by performing the solu-- tion polymerization continuously, completely filling up the polymerization apparatus with the reaction mixture and applying a pressure of 1-5 kg./cm. gauge to the reaction system by means of reciprocating pumps or other suitable devices.

Polymers employed in the present invention are composed mainly of acrylonitrile and include copolymers of acrylonitrile with copolymerizable monomers. As such monomers may be mentioned methyl acrylate, methyl methacrylate, vinyl acetate, acrylamide, methacrylamide as well as allylsulfonic acid, methallylsulfonic acid and derivatives thereof, in fact, any monomer copolymerizable with acrylonitrile.

Following the above solution polymerization process, a continuous heat treatment of the solution is carried out by applying a pressure of 1-10 kg./cm. gauge to the polymer solution in a heating vessel or vessels by means of reciprocating pumps or other suitable devices so as to prevent formation of any air foams or gel-like substances.

One typical example of such processes is illustrated in FIG. 4, wherein 1 represents a polymerization reactor to which solvent (S), acrylonitrile (M comonomers (M and catalyst (C) are continuously supplied by reciprocating pumps or such devices. The reactor is equipped with cooling and heating jackets for temperature control, a stirrer and a pressure gauge. Following the polymerization step, the resulting polymer solution is divided into two streams, A and B. One side (A) is fed to spinning step 3 through a pool tank 2. Another side (B) is fed into heating vessel 5 through a preheating zone 4. Heating vessel 5 is equipped with a heating jacket, a stirrer and a pressure gauge. Heat-treated polymer solution flows continuously to cooling zone 6, pool tank 7 and finally to spinning step 3 so as to be spun together with A. The solvent used is recovered from the spinning process as in 8 and reused after concentration and purification.

The two types of polymer solutions thus obtained can be extruded at a temperature of preferably 10-30" C. into 'a coagulating bath composed of 10-40% of-the same saline constituents as those in the solvent by the use of a conjugate-type spinnere't. The spun gel-tow thus obtained is washed with water, then heat-stretched under wet or dry conditions and relaxed in a suitable medium such as hot air, super-heated steam, saturated steam, etc. However, it should be noted that spinning processes applied in the present invention are not limited to those above mentioned.

The invention is further described with reference to the following examples, wherein all parts and percentages are by weight unless otherwise stated.

EXAMPLE 1 A copolymer solution of 92% acrylonitrile, 7.0% methyl acrylate and 1.0% sodium methallyl sulfonate in aqueous 57% zinc chloride solution containing 0.08% of zinc oxide was obtained by solution polymerization at 55 C. using ammonium persulfate as the polymerization initiator. Half of the solution was heated at 120 C. for 40 min. Viscosities of the original solution and the heattrea-ted solution were 145 and 130.5 poise at 45 C. and the T of the fibers thereof were 92 C. and 85 C., respectively. These two polymer solutions were extruded together at 20 C. into aqueous 15% zinc chloride solution through a side-by-side type conjugate spinneret (4500 holes, having a diameter of 0.14 mm.) at a rate of 200 cc./min., using separate gear pumps. The spun gel-tow was stretched 2 times its original length while being washed with water, then stretched times its length (giving a total stretch of times the original length) in boiling water, dried at 120 C. and relaxed in super-heated steam at 220 C.

The composite fibers thus obtained produced 23.4 spiral crimps per 2.5 cm. of length when the fiber was immersed in boiling water for 10 minutes and dried. The yarns made from these composite fibers have good bulkiness and excellent wool-like hand due to development of spiral crimps. The laminating property of the fibers obtained was excellent.

The temperature-contraction curves illustrated in FIG. 1 correspond to that of fibers of this example.

EXAMPLE 2 A co-polymer solution of 90% acrylonitrile, 8.5% of methyl acrylate and 1.5% sodium allyl sulfonate, in which the co-polymer concentration was 9.1%, was prepared by the continuous solution polymerization at 45 C. in an aqueous 58% zinc chloride-sodium chloride mixed salt solution (46% zinc chloride, 12% sodium chloride) containing 0.01% of zinc carbonate calculated as zinc oxide, using hydrogen peroxide as an initiator.

Half the polymer solution thus obtained was then continuously heat-treated at 110 C. for 80 min. The two solutions were then spun in accordance with Example 1. The obtained composite fiber produced 18.6 spiral crimps per 2.5 cm. of length when the fiber was treated with hot water at 100 C. for 10 min. The difierence in T before and after the heat treatment was 6 C. Further, when the polymer solution was heated at 110 C. for 1 80 rnin., the difference in T increased to 12 C. and 36.4 spiral crimps per 2.5 cm. were observed in the fiber produced. Even when fiber thus obtained was subjected to tension and relaxing treatment 10 times in boiling water, delamination 'was not observed.

The composite fiber obtained by the conjugation spinning of said original polymer solution and a solution of co-polymer comprising 90% of acrylonitrile, 8.5% of acrylamide and 1.5% of sodium all'yl sulfonate produced 23.5 spiral crimps per 2.5 cm. However, 42% of the fiber was delaminated by same tension and relaxing treatment as above.

EXAMPLE 3 90 parts of acrylonitrile, 8.5 parts of methyl acrylate, 1.5 parts of methallyl sulfonic acid sodium salt and 0.8 part of ammonium persulfate as a catalyst were dissolved in 900 parts of aqueous 58% zinc chloride solution containing 0.05% of zinc oxide. The mixture thus obtained was continuously fed into a polymerization apparatus kept at 45 C. under an internal pressure of 3 kg./cm. without permitting any empty space. A uniform and foamless polymer solution was obtained continuously after a mean residence time of 5 hours. The conversion was 97% and the viscosity of the solution was 145 poise at 45 C.

Half of the polymer solution thus obtained was fed continuously into a heating apparatus having a stirrer 'kept at 110 C. under internal pressure of 5 kg./cm. without permitting any empty space so as to prevent foams and gel-like substances from forming. A heattreated foamless and uniform solution having a viscosity of 130 poise was continuously obtained after a mean residence time of 2 hours. T of the fibers made from these solutions were C. and 76 C., respectively.

These two types of polymer solutions were spun into an aqueous 18% zinc chloride solution by the use of a side-by-side type conjugate spinneret (7800 holes, having diameters of 0.14 mm.) at 20 C. The spun gel-tow was stretched 2 times its original length during washing with water, then dried at C., stretched 5.5 times on heated roller at 160 C. and finally relaxed in super heated steam at 210 C.

The composite fiber thus obtained produced 21.5 spiral crimps per 2.5 cm. of length after treatment with hot water at 100 C. for 10 min. The fiber obtained had good laminating properties between the two components. When yarn made from the fiber was treated with steam at 103 C., the product had good bulkiness and excellent woollike hand due to the development of spiral crimps and the dyed end product had no nettled appearance, which was often observed in conventional acrylic composite fibers.

EXAMPLE 4 To 1000 parts of an aqueous salt solution containing 55% zinc chloride, 4% sodium chloride and 0.02% zinc oxide were added 89 parts of acrylonitrile, -10 parts of vinyl acetate, 1 part of sodium allylsulfonate and then 0.15 part of hydrogen peroxide as catalyst. The mixture thus obtained was continuously fed into polymerization apparatus kept at 50 C. under internal pressure of 4 kg./cm. gauge without permitting any empty space. A foamless, uniform and transparent polymer solution was obtained continuously after a mean residence time of 4 hours. Conversion was 96%, and the viscosity of the solution was 126- poise at 45 C.

Half of the polymer solution thus obtained was fed continuously into a heating apparatus kept at C. under an internal pressure of 6 kg./cm. gauge without permitting any empty space, so as to prevent the formation of any foam or gel-like substances. A heat-treated foamless and uniform polymer solution was obtained continuously after a mean residence time of 1 hour.

These two polymer solutions were spun into a coagulating bath comprising 20% of the same saline constituents as were present in the solvent by the use of a side-by-side type conjugate spinneret as described in Example 1. The spun gel-tow was stretched 2 times its original length during washing with water, then stretched 6 times in boiling water (for a total of 12 times the original length), dried and finally relaxed in super-heated steam at 150 C. The diffeernce in T of the fibers thereof obtained from the treated and untreated solution was 7 C.

The composite fiber thus obtained (3 denier) produced 17 spiral crimps per 2.5 cm. of length after treatment with boiling Water for 10 minutes. When the fiber was mixed into a conventional acrylic high-bulk yarn,.excellent woollike hand feel and good appearance were obtained in the end products.

The composite fiber has good laminating properties of the two components and the dyed end-products had no nettled appearance which was often observed in the con- 'ventional acrylic composite fiber.

Furthermore, when the polymer solution was heated to C., the difference in T increased to 12 C. and 32 spiral crimps per 2.5 cm. of length were observed in the fiber products. The fiber thus otbained gave excellent wool-like hand and bulkiness in end-products, which were blended with conventional acrylic fibers.

EXAMPLE 5 To 1000 parts of an aqueous 59% mixed salt solution (zinc chloride 55%, sodium chloride 4%) containing 0.06% of zinc oxide, 89.5 parts of acrylonitrile, 9.5 parts of methyl acrylate and 1 part of sodium methallyl sulfonate were added. The mixture thus obtained was continuously fed into a polymerization apparatus without permitting any empty space. 0.3% of sodium persulfate and 0.7% of sodium bi'sulfide were continuously added while maintaining an internal pressure of 4 kg./cm. gauge in the apparatus. After the continuous redox polymerization at 50 C. and a mean residence time of 3 hours, a foamless and uniform polymer solution having a viscosity of 152 poise was obtained at a conversion rate of 98%.

Half of the polymer solution thus obtained Was heattreated under the same conditions as Example 3 and a foamle'ss and uniform heat-treated solution having a viscosity of 139 poise was obtained. T of the fibers made from these solutions were 83 C. and 70 C., re-. spectively.

These two types of polymer solutions were spun into a coagulating bath comprising 23.3% of zinc chloride and 1.7% of sodium chloride at 20 C. by using a spinneret as described in Example 3. The spun geltow was stretched 2.5 times during washing with water at 30 -6O C., dried at 100 C., then stretched times in saturated steam at 0.8 lcg./cm. gauge and finally relaxed in saturated steam at 1.2 kgJcm." gauge.

The fiber thus obtained was highly white and produced 37 spiral crimps per 2.5 cm. of length by treatment with hot water at 100 C. for 10 min. The fiber, after relaxing, was again stretched 1.2 times its length. The esulting fibers produced 44 spiral crimps per 2.5 cm. by treatment with hot water.

What we claim is:

1. In a method for producing acrylic composite fibers by the conjugate spinning of an aqueous solution of an acrylonitrile polymer in a zinc chloride solvent, said acrylonitrile polymer being a homopolymer of acrylonitrile or a copolymer of acrylonitrile with a monomer copolymerizable therewith, the improvement comprising:

separating said acrylonitrile polymer solution into a first portion and a second portion;

heat-treating said first portion at a temperature of from about 60 to about 150 C. in the presence of a concentrated aqueous zinc chloride solvent solution containing a basic compound in an amount by weight, calculated as zinc oxide, based on the weight of said solvent solution, of from about 0.005 to about 0.2%, for a period of time such that the dilference in the temperature at which a fiber exhibits a maximum contraction in an aqueous 80% (v./v.) dimethyl formamide solution, between a fiber produced from the resulting heat-treated first portion and a fiber produced from the untreated second portion, is from about 5 to about C.; and

conjugate spinning together said heat-treated first portion and said second portion to thereby produce said acrylic composite fibers.

2. The method of claim 1 wherein the acrylonitrile polymer solution is prepared, without the formation of any foam .or gel-like substances, by continuous solution polymerization comprising filling a polymerization apparatus with a reaction mixture, applying a pressure of from about 1 to about 5 kg./cm. gauge to the reaction system and continually heating the solution thus produced while applying a pressure of from about 1 to about 10 kg./cm. gauge to the polymer solution in at least one heating vessel, so as to prevent the formation of said foam or gellike substances, said reaction mixture comprising acrylonitrile, solvent and catalyst, and at least one monomer copolymerizable with said acrylonitrile if a copolymer of acrylonitrile with said monomer is to be formed.

, 3. The method of claim 1 wherein the heat treatment of said first portion is carried out at a temperature of from about to about C.

4. The method of claim 1 wherein the basic compound is selected from the group consisting of zinc oxide, zinc carbonate, sodium hydroxide and sodium carbonate.

5. The method of claim 1 wherein the total salt content in said concentrated aqueous zinc chloride solvent solution is from about 50 to about 65 weight percent.

6. The method of claim 5 wherein said concentrated aqueous zinc chloride solvent solution further contains at least one member selected from the group consisting of sodium chloride, magnesium chloride and ammonium chloride.

7. The method of claim 1 wherein said monomer copolymerizable with said acrylonitrile is at least one monomer selected from the group consisting of methyl acrylate, methyl methacrylate, vinyl acetate, acrylamide,

methacrylamide, allyl sulfonic acid, methallyl sulfonic acid and derivatives thereof.

8. The method of claim 1 wherein said conjugate spinning is conducted at a temperature of from 10 to 30 C.

9. The method of claim 1 wherein said heat-treated first portion and said second portion are conjugately spun together into a coagulating bath, and further comprising washing the resulting fibers with Water while stretching said fibers, drying said fibers, heat-stretching said fibers and heat-relaxing said fibers.

10. The method of claim 9 wherein said coagulating bath comprises an aqueous solution containing from about 10 to about 40% by weight of at least one member selected from the group consisting of zinc chloride, sodium chloride, magnesium chloride, and ammonium chloride.

11. The method of claim 9 wherein said stretching step during said washing step is conducted in an amount of from about 2 to about 2.5 times the original length of said fibers, and wherein said water washing step is conducted at a temperature of from about 30 to about 60 C.

12. The method of claim 9 wherein said heat-stretching step is conducted in an amount of from about 5 to about 6 times the length of the fibers after the stretching step during said water washing step, at a temperature of from about 100 to about 160 C.

13. The method of claim 9 wherein said heat-relaxing step is conducted in super-heated steam at a temperature of from about to about 220 C.

References Cited UNITED STATES PATENTS 2,439,815 4/1948 Sisson 264-Dig, 26 3,084,993 4/ 1963 Dawson et al. 2'64-Dig. 26 3,135,812 6/1964 Taniyama et al. 264-182 3,209,402 10/1965 Riley et al. 18-8 3,408,277 10/1968 Martin et al. 264-171 3,485,913 12/1969 Yamada et al. 264-210 F FOREIGN PATENTS 9,164 6/1964 Japan 264-182 525 1/1968 Japan 264-Dig. 26 10,171 4/1968 Japan 264-Dig. 26 22,327 9/ 1968 Japan 2-64-Dig, 26

JAY H. WOO, Primary Examiner U.S. Cl. X.R. 

